Piezo-electric crystal circuits



Dec. 10, 1929. F. B. MONAR 1,739,165

PIEZO ELECTRIC CRYSTAL CIRCUITS Filed Sept. 12, 1925 gnuc'nfoz Fred .B. MO/mr Patented Dec. 10, 1929 PATENT FFEQE FRED B. MONAR, OF WASHINGTON, DISTRICT OF COLUMBIA PIEZO-ELECTRIC CRYSTAL CIRCUITS Application filed Scptember 12, 19525. Serial No. 55,969.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED AFRIL 30, 1928; 370 0. G.

My invention relates broadly to piezoelectric crystal circuits and more particularly to methods of improving the control of crystale that are normally poor oscillators..-

In practice it is found that only about five per cent of crystals tested show excellent oscillating properties. Of the remainder about twenty-five per cent are usable, and the rest are either poor oscillators or no oscillators at all. This condition creates a situation where it is necessary to resort to some means of improving the lower grades of crystals by compensating for the difference in oscillating properties.

The object of my invention is to compensate for the difference in oscillating properties between crystals by reinforcing the true oscillations of a crystal.

Another object of my invention is to reinforce the oscillations of a crystal without affecting the true frequency generated by the crystal.

A further object of my invention is to provide such a reinforcement of crystal oscillations without any change in the plate and grid voltages of the vacuum tube controlled by the crystal.

Further objects of my invention will appear more fully hereinafter.

For the accomplishment of these objects I make use of the feed-back principle, an inductance being placed in the plate circuit of the tube having an optimum value for the frequency at which the circuit is operative, and another inductance in series with the crystal and so coupled to the first inductance that the phase relationship permits a feedback strengthening the true crystal oscillation. This coupling is found to be critical and has to be much less than that required in an ordinary vacuum tube oscillating system; if too great, the true frequency generated by the crystal is affected and local self oscillations arise. Accordingly, in practice, it is made just enough to make up for the diflerence in the oscillating properties of a poor crystal from those of an excellent crystal. By this means the maximum output from all crystals possessing oscillating properties is obtained without resort to the increase in the plate or grid supply voltages or the loss of the true frequency of the crystal.

My invention consists substantially in the construction, combination, and arrangement of parts as will be more fully hereinafter set forth as shown and finally pointed out in the appended claims.

in the accompanying drawing forming part of this specification and in which the figure represents a schematic arrangement of my circuit a crystal 1 with its metal contacts is connected to the grid and the negative terminal of the filament of the vacuum tube 5. Across these connections of the crystal is the radio frequency choke coil2 and the C battery 3. An inductance 4c is inserted in the circuit between the lower crystal plate and the tube filament. A l attery 6 supplies the heating current to the filament of the tube 5 through the rheostat 7. The tube plate is furnished with energy from the battery 8, through the inductance of the oscillatory circuit 10, which circuit also includes the in ductance l A radio frequency by pass condenser 9 connects the low potential radio frequency side of the oscillating circuit with the filament. I

The two inductances 4 and 4 constitute the coupling whereby energy is fed from the plate circuit to the crystal. The inductance 4 is constructed for the frequency at which the oscillator is designed to operate, as above stated, and provides for the transfer of energy not exceeding the critical value necessary to bring the crystal to its maximum output Without affecting its true frequency and creating local self oscillations.

It will be understood that the above description and accompanying drawings comprehend only the general and preferred embodiment of my invention and that various minor details in construction and arrangement of parts may be made within the scope of the appended claims and without sacrificing any of the advantages of my invention.

The invention herein described may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon or therefor.

Having thus described my invention What' I claim is:

1. In a piezo electric oscillator the combination of a Vacuum tube having a filament, grid-filament and plate-filament circuits, the combination of an inductance and a source of potential in series in the grid filament circuit, a piezo-electric crystal and a second inductance in series With each other and connected in parallel With the first mentioned inductance and the source of potential, a resonant circuit in the plate-filament circuit and means for coupling said resonant circuit to one of the inductanccs in the grid filament circuit to produce increased output of said 7 picZo-electric crystal.

2. In a piezo electric oscillator the combination of a vacuum tube-having a filament, grid-filament and plate-filament circuits, the combination of an inductance and a source of potential in series in the grid filament circuit, a piezo-electric crystal and a second inductance in series With each other and connected in parallel with the first mentioned inductance and the source of potential and a resonant circuit in the plate-filament circuit, said resonant circuit consisting of a plurality of inductances and a capacity in series with each other one of said inductances coupled to the second inductance in the grid-filament circuit and another of said inductances in said resonant circuit forming a portion of the plate-filament circuit of said vacuum tube.

' FRED B. MONAR. 

